This invention relates generally to a method and apparatus for controlling the speed of electronically commutated motors and is particularly useful for controlling motors used to drive digital disk storage devices.
The prior art is replete with various systems for controlling the rotor speed of electronically commutated motors. One frequently used method is to control the voltage drop across a regulating element connected in series with the motor windings to thus vary the effective voltage applied across the motor windings. The regulating element can be operated either in a linear mode or in a pulse mode by means of pulse-width or pulse-frequency modulation. The pulse mode provides a time average voltage drop across the regulating element that determines the effective voltage made available to the motor windings.